A comparative study of hot ductility of unadded and Ce-added SA508-4N RPV steels

Abstract

The hot ductility of the SA508-4N RPV steel samples, unadded and added with 0.015 wt.% Ce, has been investigated in the range 750–1000 °C. The study is carried out by using a Gleeble machine and various evaluation techniques. Between 750 and 1000 °C, the steel is located in the single-phase austenite region. In this region, the unadded steel presents a hot ductility trough between 750 and 900 °C and the reduction of area (RA) at the trough bottom is rather small, being just ~50% at 850 °C. However, the hot ductility of the steel can be substantially enhanced by a trace addition of Ce, so that the hot ductility trough is eliminated for the Ce-added steel. In the testing temperature range, the RA values of the Ce-added steel are all higher than ~75%. Microanalysis demonstrates that grain boundary segregation of Ce plays an important role in the improvement of hot ductility by enhancing the intergranular cohesion and thus suppressing the boundary sliding. Furthermore, the initial temperature of dynamic recrystallization occurrence can be lowered to ~850 °C from ~900 °C by the Ce addition. This implies that Ce can also facilitate the occurrence of dynamic recrystallization of SA508-4N RPV steel, thereby raising its hot ductility performance.

Keywords

• Hot ductility
• RPV steels
• Grain boundary sliding
• Grain boundary segregation
• Dynamic recrystallization